Energy Vanguard Blog

Do Power Factor Correction Devices Save Energy?

Today we're running a guest post by Chris Kaiser of Mapawatt.com. I met Chris recently because we're both blogging from the great city of Atlanta, and our blogs complement each other well. Here at Energy Vanguard, we focus mainly on building science and energy auditing/rating. Mapawatt concentrates on energy monitoring and energy efficiency products.

Chris's post covers the power factor correction device scam, and why you definitely don't want to throw your money away buying such a device. In addition to his post and the links he provides, another one on this topic you might want to check out is the very geeky NLCPR website, which, by the way, also has a page describing how to make your own Blower Door. ab3

Part of our goal with the Mapawatt Blog is to review the best products that can save energy and water in your home. Product developers know that as energy costs rise, consumer’s budgets get tightened, and people start to care more about their environment (the trifecta of sustainable drivers), those consumers are going to want products that help them save energy. But do all these products live up to their claims?

One of these products is a power factor correction device and can be seen here. This product claims:

Residential customers throughout North America could see a realized savings of 8% – 10% typically and as much as 25% on their electrical usage (and thus power bills).

However, I’m not buying it. There are two great resources on-line that address this same issue. One is Energy Star (page no longer available) and the other is a blogger I’ve been reading for 4 years and has a great section on electricity, Michael Bluejay. Both of these resources say power factor correction really won't help on your residential bill. It can make a difference for certain industrial users who may be billed by the Utility for peak demand, but this is another story (and it is addressed in the Bluejay article).

To go a little deeper, the formula for Power Factor (PF) is below:

PF = Real Power (Watts) ÷ Apparent Power (VA)

- or -

Watts = PF*Amps*Voltage = PF * Apparent Power

The power factor correction devices are said to improve the second half of the above equation, the Apparent Power. However you don’t pay your utility for Apparent Power. You pay them for Real Power (Watts). Apparent Power is defined as the total power in an AC circuit, both dissipated AND returned! (Scroll to the bottom of this link to view the power triangle and description of Apparent, Real and Reactive power). This means that if you currently have a poor power factor, your Apparent Power is higher, but all this means is that you are returning more unused electrons to the utility! But since they only charge you for used electrons (dissipated electrons = Real Power = Watts) you don’t give a hoot about your Apparent Power!

Let’s take an example of 2 completely identical motors sitting side by side. Both of these motors have the exact same efficiency and operate at 1.2 kW. The first motor doesn’t have a power correcting device. The second motors does have PF correcting device.

Using the equation above we can show the amps (current) that will be dissipated in motor 1:

1.2 kW = .7 *120V * A → A= 14.29

And we can do the same thing for motor 2:

1.2 kW = .999*120V*A → A=10.01

But this doesn’t mean you’ll pay less to the utility! All this shows as that your power factor increases (gets better) your amperage decreases, but the Real Power (Watts = what the utility charges you) stays the same! Therefore no matter your power factor, in residential settings the utility is still going to show that you took the same amount of Real Power off of the power lines, so that is what you pay.

I’m not the only site questioning the validity of Power Factor correction devices. Open4Energy has a great review of Open4Energy: Power factor correction Scam. I should note that it is in their “scam” section!

Comments

We have gathered data from the KVAR Energy Controllers installed for our customers that indicate savings. Our data includes factoring lifestyle changes and climate conditions. We personally have a KVAR EC on our home and are experiencing a reduction in KW usage when comparing the same periods from one year to the next.

Kathleen, I'm afraid there must be other factors contributing to your savings because these power factor correction devices can have no effect on home energy use. They don't work. See the article above.

Posted @ Tuesday, August 24, 2010 1:34 PM
by Allison Bailes

This depends on the PFC figure which needs to be lower than 0.95 at 0.85 good savings will be made and the bill must be in KVA not KW.

Lee, you hit the nail on the head. Utilities bill residential customers by the kilowatt-hour (kWh), not the kilovolt-amp-hour (kVAh), so these devices will do nothing to lower the bills on homes.

Drilling a little deeper, the utility actually determines residential customers' bills by the following formula:

kWh = Power Factor x current x voltage x time

If you put a power factor correction device on your home, the power factor goes up, the current goes down, but the product (Power Factor x current) stays the same, which means that it will not affect your bill one bit.

We have come across many of these devices and even the same one in the picture.

If you have lets say a 20+ year old appliances and are charged a KW (demand)plus kWh on your bill from your electric provider. One might say the device is worth the money. However, If you have high efficiency appliances and are only billed kWh, this device will cost you more to run than what it claims to save don't be fool by the promise it will save...Remember it only works when a low efficiency appliances is running just like the little 1hp motor video.

Don't waste your money in my opinion upgrade your old appliances and the home insulation R-values, and this will add true value and true comfort to your home or business...

Two different location Examples:

We had one person pay $500 for one of these little devices claiming to save 30% on utility usage. After we test the device at the customer location it did correct PF around 3% at best only when the old A/C system was running, however cost more to keep the KVAR on than what it claimed to save when the A/C system was off.

The second person home we reviewed had major duct leaks and low insulation found. Customer had ducts repaired and more insulation blown in the attic and saved on average 27% plus they were more comfortable and the A/C system did not have to work as hard; which will prolong its life and reduce maintenance costs...

Review facts before wasting any time or money on one of these KVAR units...or check with your power provider before you install one of these.